Method of separating suspension, in particular for waste water treatment

ABSTRACT

A method of separating suspension, in particular for treatment of waste water, wherein the flocculating suspension is separated from the liquid by filtration in a fluidized layer in a sludge blanket wherein the flocks are created from the separated suspension and the fluidization is maintained by the rising stream of liquid, while the liquid with suspension enters the fluidized layer from the bottom and the liquid freed from suspension is discharged above the surface of the sludge blanket represented by the interface between the fluidized layer and the liquid without suspension. The thickened separated suspension in form of flocks from a sludge blanket is withdrawn from the zone of the fluidized layer, the velocity of upward flow in the fluidized layer essentially decreasing in the upward direction. The apparatus for performing this method contains an upward widening separator ( 1 ) provided by inlet ( 5, 38, 59 ) of treated suspension in its bottom part, and by means for withdrawing the liquid without suspension at its top. A separator ( 1 ) the inner space of which contains a separation space is provided with at least one withdrawal spot of the thickened suspension from separation space that is arranged above the inlet ( 5, 38, 59 ) into separator ( 1 ), predominantly at its outer wall ( 2 ) or outer walls ( 33, 34, 50, 51 ) and under the surface of the sludge blanket.

FIELD OF THE INVENTION

The invention relates to a method of separating suspension, inparticular for treatment of waste water, wherein the flocculatingsuspension is separated from the liquid by filtration in a fluidizedlayer in a sludge blanket wherein the flocks are created from theseparated suspension and the fluidized state is maintained by the risingstream of liquid, while the liquid with suspension enters the fluidizedlayer from the bottom and the liquid freed from suspension is dischargedabove the surface of the sludge blanket represented by the interfacebetween the fluidized layer and the liquid without suspension. Furtherit relates to an apparatus for performing this method containing anupward widening separator that is provided with the inlet of liquid withsuspension in its bottom part, and a means for withdrawal of liquidwithout suspension in its upper part.

DESCRIPTION OF THE PRIOR ART

One of the most advanced methods for the separation of flocculatingsuspension during the purification and treatment of water is fluidfiltration in a sludge blanket. The sludge blanket consists of afluidized layer of flocks that are created by agglomeration of particlesof the separated suspension. Water with suspension to be removed entersthe sludge blanket by upward streaming. This flow sustains the layer offlocks in fluidized condition. During the throughflow of water withsuspension through the fluidized layer the particles of suspensioncontact flocks with following capturing of suspension particles due totheir adhesion to the flocks. This filtration relieves water fromsuspension that is transformed into flocks that are substantially largerthan the inflowing suspension particles.

The fluidized layer creates a top interface between the fluidized layerand the liquid without suspension, the so-called surface of sludgeblanket, the liquid freed from separated suspension being withdrawnabove the surface of sludge blanket. The interface is established, ifthe flow velocity of liquid directly above the interface is lower thanthe velocity of not retarded sedimentation of separate particlescreating the fluidized layer. Since the flocks created in the sludgeblanket by agglomeration of suspension are substantially larger than theparticles of inflowing suspension, this velocity substantially exceedsthe sedimentation velocity of the separated suspension. The withdrawalof clear liquid shall be sufficiently spaced from the surface of sludgeblanket, for preventing flocks from being dragged out of the sludgeblanket due to irregularities of withdrawal. Due to that a layer ofclear liquid in the separation zone above the sludge blanket is alwaysindispensable.

The fluidized layer shall be supported from the bottom. A frequentlyused method of supporting the fluidized layer is hydrodynamic supportconsisting in that the quick flow of liquid under the fluid layerprevents its fall down. In such case the flow velocity of liquid in thefluidized layer decreases in upward direction.

A sludge blanket with flocks created by flocculating suspension ischaracterised by dynamic balance determining the size of flocks at thegiven spot. By catching particles of suspension and by agglomeration thesingle flocks grow, whereas large flocks are desintegrated to smallerones under the influence of hydrodynamic forces. The fluidized layer forits part affects the liquid flow, thus establishing feedback.

The continuous interception of the suspension results in the increase ofthe total volume of flocks and, accordingly, the superfluous flocksshould be removed from the sludge blanket. Thus the separated suspensionis withdrawn from the sludge blanket in form of excess flocks.

Two types of sludge blanket are known: the fully fluidized one,specified also as perfectly fluidized, and the partially fluidized one,specified also as imperfectly fluidized. They differ as to the velocityof liquid at the surface of the sludge blanket and as to the type ofwithdrawal of excess flocks. In a partially fluidized sludge blanket thevelocity of liquid at the surface of the sludge blanket is smaller thanthe limit of fluidization and the excess flocks are withdrawn from thebottom, in a fully fluidized sludge blanket the velocity of liquid atthe surface of the sludge blanket exceeds the limit of fluidization andthe excess flocks are withdrawn from the surface of the sludge blanket.

Due to the fact that the velocity of liquid tends to be slower than thefluidization limit at the surface of the partially fluidized sludgeblanket, failures of fluidization are encountered there. Largeagglomerations of flocks are created that fall down through thefluidized layer. Their falling down leads to rising currents in thevicinity, thus increasing the local velocity of upward flow, whichcontributes to the maintaining of fluidization in other zones close tothe sludge blanket surface. Since the average velocity of the upwardflow in a fluidized layer increases in the downward direction, someagglomerates are decomposed in the quicker flow and their flocks returnback to the sludge blanket. Some agglomerates, however, fall throughunder the fluidized layer wherefrom they are removed. Within a certainrange of parameters a balance is achieved between the amount ofsuspension flowing into the sludge blanket and the amount of suspensionfalling out of the sludge blanket and withdrawn by way of the describedmechanism. If the amount of incoming suspension exceeds the amount ofsuspension that falls out, the volume of the sludge blanket increases,and if it exceeds the capacity of the plant, the sludge blanket startbeing washed away into the withdrawal of purified water, i.e. it flowsover. If the amount of incoming suspension is smaller than the amount ofthe suspension falling out, the volume of sludge blanket decreases, andif it drops under a critical value, the sludge blanket drops under theseparator or, in other words, it falls out of the separation space.

The concentration of flocks in the sludge blanket depends upon thevelocity of the upward flow. The lower is the flow velocity the higheris the concentration. The concentration of flocks in the agglomeratesfalling out of a partially fluidized sludge blanket is higher than whatwould correspond to the velocity of fluidization limit. That is why theconcentration of separated suspension removed from a partially fluidizedsludge blanket can be higher than the concentration of a suspensionremoved from a fully fluidized sludge blanket. On the other hand,however, the flow velocity at the surface of the sludge blanket and,accordingly, the hydraulic performance of a fully fluidized sludgeblanket is higher than that of a partially fluidized sludge blanket.That is why the use of fully fluidized sludge blanket is favourable forthe separation of diluted suspensions, whereas the partially fluidizedsludge blanket is suitable for separating concentrated suspensions.

For this reason the fully fluidized sludge blanket has been used in thechemical treatment of water where the concentration of suspension, as arule, makes tenths of grams of dry matter per cubic meter. The velocityof liquid flow at the surface of the sludge blanket achieves currentlythe values of 4–4.5 m per hour while the suspension withdrawn from thesurface of the sludge blanket is four times to eight times thicker, thewithdrawn flocks being later subjected to secondary thickening bysedimentation. A partially fluidized sludge blanket can be used inbiological treatment of sewage where current concentrations of thesuspension make 4 to 6 kg of dry matter per cubic meter and theseparated thickened suspension is returned back into the treatmentprocess. The flow velocity of liquid at the surface of the sludgeblanket currently achieves values of 0.8–1 meter per hour and thewithdrawn suspension may thicken from 1.5 times up to the double.

Of course all limit values depend upon a number of parameters, of whichespecially the water temperature and the character of suspension haveremarkable influence. By monitoring many plants over a number of yearsthese parameters were found to influence the limit values within 10 to30 percent, as a rule.

The separation spaces wherein the described filtration in the sludgeblanket takes place have usually the form of an upwards broadening cone,pyramid or prism, ensuring the decrease of liquid flow velocity in theupward direction. They are limited by inclined walls, usually 52 to 60degrees inclination which, on the one hand side, prevents flocks fromdepositing layers on these walls and, on the other hand, it providessufficient surface for the surface of sludge blanket. The stream ofliquid in these separation zones has, due to their shape, in addition tothe vertical upward component, also a horizontal component directed tothe inclined walls. Against the vertical component of flow the flocksare subjected to gravitation forces in downward direction. Beingcombined these forces result in a horizontal force that urges the flocksin direction to the inclined walls. Owing to that the concentration ofsuspension increases at the inclined walls, resulting in downwarddensity streams along these walls. In a partially fluidized sludgeblanket the agglomerates of flocks falling down continue, after havingcontacted the inclined wall, also as density streams. The concentrationof suspension in the density streams is then further influenced by twocontrary effects: on the one hand, due to the gravitation force, furtherthickening of the suspension takes place in the density stream flowingdown along an inclined wall; on the other hand the counterflow of liquidstreaming towards the separation space in the upward direction washesthrough the density flow diluting, on the contrary, the suspension inthe density flow.

The separators for the sludge blanket are further equipped with thewithdrawal of pure liquid without suspension at the top, usually in theform of overflow troughs or perforated tubes, and at the bottom they areprovided with inlet of liquid with suspension to be separated.

The simplest solution of this inlet is a simple hole connecting theseparation space with another functional space, such as an activationspace in case of biological waste treatment or a coagulation space incase of chemical water treatment. However, also more complex solutionsare known, such as in form of inclined feeding channels along the wallsof the separation space, or in form of a central inlet pipe passingvertically through the centre of the separation space. Such inletchannels or pipes are then connected with another functional space fromwhich the liquid with suspension usually flows down to the spot of theactual entry to the separation space in which the liquid flows upwards.If the overall arrangement of the entry into the separation space ismore complex, then, with regard to the above described mechanism ofhydrodynamic support of the fluidized layer of the sludge blanket, underthe concept of entry to the separation space the horizontal surface isunderstood at the upper level of the hole through which water flows tosuch inlet to the separation space. The upper part of the separationspace for a fully fluidized sludge blanket is provided with withdrawalof separated suspension delimiting the position of the sludge blanketsurface, whereas for a partially fluidized sludge blanket the withdrawalof separated suspension is arranged under the level of entry of theliquid with suspension to the separation space. The throughflow area ofthe liquid with suspension entry to the separation space, as a rule,makes 2.2 to 2.5 percent of the separation space for a fully fluidizedsludge blanket, and 10 to 15 percent of the same for a partiallyfluidized sludge blanket. The larger the throughflow area of the entryto the separation space in a partially fluidized sludge blanket, thehigher concentrations of suspension can be separated by this sludgeblanket, but the higher also the limit for this sludge blanket to fallout.

The described principles elucidate yet another substantial differencebetween a partially fluidized sludge blanket and a fully fluidized one.The height of sludge blanket surface in a fully fluidized sludge blanketis constant, and if there are any changes of throughflow orconcentration of the entering suspension, only the concentration ofwithdrawn thickened suspension varies. Exceeding the maximum performanceis manifested by taking flocks out of the sludge blanket and by itssurface being washed out. In a partially fluidized sludge blanket itssurface height varies along with changes of throughflow and ofconcentration of the entering suspension, and exceeding the maximumperformance is manifested by the rise of the sludge blanket up to thewithdrawal level of purified liquid, with following overflow of thesludge blanket to the withdrawal.

Operation experience has shown the sludge blanket is properly functionalalways within a certain range of design parameters only. If thethroughflow drops under about 50 percent of the rated performance in afully fluidized sludge blanket used for chemical water treatment,disturbances of fluidization occur that have the tendency to get worse,and within a certain time they result in functional failures. If theconcentration of activated sludge drops under 1–2 kg of dry matter percubic meter in case of a partially fluidized sludge blanket used forbiological treatment of water, a sludge blanket is not established inthe separation space, or if the concentration of suspension has droppedunder the mentioned limit, the sludge blanket is likely to fall out ofthe separation space, i.e. it will sink under the separation space.

The principles of fully fluidized sludge blanket and variousarrangements of corresponding apparatuses are described, e.g., in theCzech Patent Specification No 88634 (S. Mackrle, V. Mackrle, I.Tesa{hacek over (r)}ík, V. Mi{hacek over (c)}an, Reactor for watertreatment by sludge blanket) and the Czech Patent Specification No123929 (S. Mackrle, V. Mackrle, O. Dra{hacek over (c)}ka, L. Paseka,Clarifier for water treatment by coagulation and filtration by perfectlyfluidized sludge blanket) and its corresponding Canadian PatentSpecification No 769769. A partially fluidized sludge blanket withspontaneous falling down of separated suspension back to the treatmentprocess is described, e.g., in the Czech Patent Specification No 159811(S. Mackrle, V. Mackrle Modular apparatus for biological treatment oforganically polluted liquids) and its corresponding foreign patentspecifications, the Canadian No 921626 and the U.S. Pat. No. 3,627,136,and is also described in the Czech Patent Specification No 173893 (S.Mackrle, V. Mackrle, O. Dra{hacek over (c)}ka, Reactor for biologicalpurification of liquid, in particular sewage water) and itscorresponding foreign patent specifications, the Canadian No 1038090,German No 2456953, French No 7439337 and the Japanese No 1044405. Apartially fluidized sludge blanket with the application of sucking awaythe fallen down separated suspension is described in the Czech PatentSpecification No 275746 (S. Mackrle, V. Mackrle Method of biologicalactivation purification of water and apparatus for performing the same),with corresponding U.S. Pat. No. 5,032,276 and EP 345669.

SUBSTANCE OF THE INVENTION

The drawbacks of the prior art are substantially eliminated by themethod according to the present invention characterised in that thethickened separated suspension in form of flocks from the sludge blanketis withdrawn from the zone of the fluidized layer, the velocity ofupward flow in the fluidized layer decreasing essentially in the upwarddirection.

It is beneficial if the thickened separated suspension in form of flocksof the sludge blanket is withdrawn from an outer boundary zone of thefluidized layer and if the velocity of flow in the upward directiondecreases both above the level of the withdrawal of the thickenedsuspension and under the same.

It is further important that the layer of the sludge blanket above thewithdrawal level of the thickened suspension functions as a partiallyfluidized sludge blanket wherein agglomerates of thickened suspensionare established that are then removed, the layer of sludge blanket underthe withdrawal level of thickened suspension functioning as a fullyfluidized sludge blanket wherein the liquid flow is distributed into thepartially fluidized sludge blanket.

It is preferable for reducing the volume of withdrawn excess suspensionif the separated thickened suspension removed from the fluidized layerforcibly moves downward while getting further thickened, and, if theconcentration of inflowing suspension exceeds 1 kg of dry matter percubic meter, the velocity of upward water flow immediately above thesurface of sludge blanket is in the range of 1.6 to 2.2 meters per hourand the water flow velocity at the entrance to the sludge blanket iswithin the range of 2 to 6 cm per second. The volume of withdrawnthickened suspension makes 1.5 multiple to 3 multiple of the volume ofwater without suspension withdrawn above the surface of the sludgeblanket.

The object of the apparatus according to the invention for performingthe described method consists in that the separator, the inner volume ofwhich contains the separation space, is provided by at least onewithdrawal spot of thickened suspension that is located above the inletto the separator, predominantly at its outer wall or outer walls andunder the surface of the sludge blanket.

It is also substantial that the withdrawal spot of the thickenedsuspension are vertically located in the middle part of the separationspace, close to at least one of its outer walls, while the separationspace within the separator essentially widens in the upward directionboth above the level of withdrawal of the thickened suspension andunderneath the same.

According to another variant of the apparatus according to the inventionit is important that the separation space within the separator, in itsbottom part, is limited at least by one, at least partially inclinedinner wall, while the space between the bottom part of the outer walland the inner wall creates a thickening space, whereas the gap betweenthe upper edge of this inner wall and the outer wall represents thewithdrawal spot of thickened suspension from the separation space. Alongwith that it is beneficial if the gap between the upper edge of theinner wall and the outer wall also creates an entry to the thickeningspace that is provided with means for withdrawing the thickenedsuspension in its bottom part.

Yet another variant is preferable wherein the means for withdrawingthickened suspension are created by a horizontally arranged collectingtube arranged adjacent to the inclined outer wall of the separator.

A contribution is offered also by an embodiment wherein the inclinedouter wall of the separator makes an angle in the withdrawal zone ofthickened suspension, the upper part above this level being moreinclined than the bottom part of the same underneath.

Considering the effectiveness of removing the thickened suspension, itis beneficial if the separator, and consequently also the separationspace, suddenly widens upwards at the place of collecting tubes, whilethe side of collecting tubes turned to the upper part of shiftedinclined outer wall is provided with apertures.

It is advantageous for the functioning of the apparatus according to theinvention that the area of entrance to the separation space makes morethan 3 percent and less than 6 percent of the surface of the separationspace at the level of withdrawal of liquid without suspension, whereasthe area of the separation space immediately under the removal level ofthickened suspension makes more than 20 percent, and immediately abovethe level of thickened suspension removal it makes less than 70 percentof the surface of the separation space at the level of withdrawingliquid without suspension. It is also preferable to maintain a verticaldistance of more than one meter between the withdrawal level ofthickened suspension and both the height of entry to the separationspace and the height of withdrawing the liquid without suspension.

It is also significant that the height of the withdrawal level ofthickened suspension above the level of entry into the separation spaceis in the range from ¼ to ¾ of the height of withdrawing liquid withoutsuspension above the entry level into the separation space.

Considering the design it is a contribution that at least one functionaltube from the group created by the collecting tubes of the thickenedsuspension, collecting tubes for withdrawing the thickened suspension,the collecting tubes for withdrawing liquid without suspension, thetubes serving as discharge, the inlet pipes of pressure air and therinsing pipes, creates also a part of the supporting structure of theouter walls of the separation space.

It is also advantageous if the angle of the upper part of the inclinedouter wall is within the range between 52° and 60° or, possibly, if theangle of the inclined inner wall is within the range between 52° and60°, whereas the angle of the bottom part of the inclined outer wall iswithin the range of 30° to 40°.

The most essential advantage of the method and the apparatus accordingto the present invention is a substantial improvement of the efficiencyof separation, which is enabled in particular by the increase of solidsload of the separation when separating a concentrated suspension, andnamely up to the double achievable by known systems of fluid filtrationusing a partially fluidized sludge blanket. This can be made use ofeither for increasing the hydraulic load and, accordingly, for enhancingthe separation capacity, or for increasing the concentration ofsuspension entering the sludge blanket or, possibly, for an optimumcombination of both these effects. Such quantitative improvement ofseparation efficiency will be a special contribution for the activationtype of biological waste water treatment regarding the savings in thedesign of integrated biological reactors. The increase of hydraulic loadowing to the application of the method and apparatus according to thepresent invention allows to cut down the separation space, and namely byup to 50 percent against the dimensions of hitherto known plants using apartially fluidized sludge blanket. This brings not only savingsrelating to the construction of the separator, but also furtherconstruction savings, such as by reducing the necessary height of theintegrated biological reactor and easier accommodation of the separatorin the reactor. The increased concentration of activated sludge in thebiological reactor is also reflected in cutting down the functionalvolumes that are necessary for biological processes and thereby alsocutting down the overall size of the reactor. The reduction of theseparator size and the optimisation of the construction and of thedimensions of the reactor allow to achieve considerable savings ofmaterial, manufacturing cost, transport, and installation. Anotheradvantage of the method and apparatus for implementing the methodaccording to the present invention is their functioning within asubstantially broader range of parameters than in the case of apartially fluidized sludge blanket. This widens the scope of utilisationof the method and the apparatus and enables their substantially improvedflexibility during operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Four exemplifying embodiments of the invention will be described, where

FIG. 1 shows the first example of embodiment of an apparatus accordingto the invention in side section,

FIG. 2 shows the first example of embodiment of an apparatus accordingto the invention in axonometric representation,

FIG. 3 is an integration of the first example of embodiment into anexemplary integrated reactor for activation treatment of waste water,

FIG. 4 is a second exemplary embodiment of the apparatus in sidesection,

FIG. 5 the second exemplary embodiment in axonometric representation,

FIG. 6 a third exemplary embodiment of the apparatus in side sectionwithin an exemplary integrated biological reactor,

FIG. 7 an axonometric representation of an exemplary embodimentaccording to FIG. 6,

FIG. 8 shows the fourth exemplary embodiment of the apparatus in sidesection and

FIG. 9 the fourth exemplary embodiment in axonometric representationwithin an exemplary integrated biological reactor.

EXEMPLIFYING EMBODIMENTS OF THE INVENTION

For full understanding the examples of apparatus are always described asparts of an exemplary integrated reactor for the activation treatment ofwaste water, with nitrification and de-nitrification by uniformsuspended activated sludge; the examples of apparatus in such exemplaryintegrated reactor serve for separating the flocculating suspension thatis produced during the mentioned treatment. The parts that arefunctionally and constructionally similar are designated with the samereference numerals in various examples of embodiment.

EXAMPLE 1

The basic part of the apparatus for the separation of flocculatingsuspension according to this invention is separator 1 in form of anupwards widening cone limited by outer wall 2 in shape of a conicalcasing (FIGS. 1, 2). The shape of the cone of separator 1 can be alsonon-continuous in the sense that it may comprise not illustrated shortcylindrical parts, or even tapered parts of opposite inclination, e.g.due to manufacturing or design reasons.

The inner space of separator 1 contains a separation space; according tothis example of embodiment the inner space of separator 1 practicallyco-incides with the separation space. The outer wall 2 comprises aninserted means for withdrawing the thickened suspension, and namely inform of a circular wound collecting tube 3 of angular section and itsupper part accommodates another means for withdrawing liquid withoutsuspension in form of circular wound collecting tube 4 of triangularsection.

The height of withdrawal level of thickened suspension above the levelof inlet 5 into separator 1 and, accordingly, into the separation space,is within the range of ¼ to ¾ of the height of the level of withdrawingliquid without suspension above the level of inlet 5 into the separationspace. It is preferable to arrange the means for withdrawing thethickened suspension to middle height of separator 1. The collectingtubes 3 and 4 can have other sections, the mentioned shapes being onlyadvantageous.

A set-back of the outer wall 2 in the diameter is provided at the levelof the lower collecting tube 3, but the outer wall 2 can be alsoperformed as a continuous conical area without any abrupt change. Thebottom part of the outer wall 2 is terminated by the inlet 5 intoseparator 1 that is performed as the entry opening.

The upper collecting tube 4 for withdrawing liquid without suspension isprovided with hole 6 at its outer inclined side, whereas the lowercollecting tube 3 for withdrawing thickened suspension is provided withholes 7 in its upper horizontal side. Both perforated tubes 3 and 4represent also construction elements creating the supporting structureof separator 1. The upper collecting tube 4 mouths into discharge 8arranging overflow 9 for maintaining constant surface 10 of water inseparator 1. The lower collecting tube 3 is connected withre-circulation pump 12 via tube 11. The outer wall 2 above the uppercollecting tube 4 can end with another shape rather than a cone, due tooperational reasons, such as a cylindrical endpiece 13. During theoperation of the apparatus the surface 14 of sludge blanket is locatedbetween the perforated lower collecting tube 3 and the perforated uppercollecting tube 4.

The described example of an embodiment for separating flocculatingsuspension creates a part of a reactor for biological activationtreatment of waste water consisting, according to this example ofembodiment, of tank 15 divided so as to form an oxic space 16 and ananoxic space 17 that communicate via connection 18. This connection 18,e.g., can be performed as a notch in the partition wall 19 separatingthe oxic space 16 from the anoxic space 17.

The oxic space 16 of the reactor according to the example of embodimentaccommodates the described separator 1 whose inlet 5 thus communicateswith the oxic space 16, whereas the outlet 20 of the re-circulation pump12 mouths in the anoxic space 17. The bottom 21 of tank 15, under theinlet 5 into the separator 1, accommodates counter-cone 22 (FIG. 3)having holes 23 in its upper part. The oxic space 16 is provided withaeration elements 24 connected with the inlet pipe 25 of pressure air(FIG. 3), whereas the anoxic space 17 is provided with inlet 26 of wastewater and agitator 27 directed between two parallel deflecting walls 28that are vertically arranged in the anoxic space 17. The inlet 26 ofwaste water and outlet 20 of re-circulation pump 12 mouth in oppositecorners of the anoxic space 17 to the bottom 21 or, possibly, to middledepth of tank 15, the connection 18 with the separation space beingperformed close to surface 10 of water in tank 15.

The described apparatus works as follows. Water with flocculatingsuspension composed of biologically activated sludge flows into theseparation space through inlet 5. In the separation space the waterflows upwards, and since the separation space in separator 1substantially widens in the upward direction, the velocity of water flowsubstantially decreases in the upward direction. Within the separationspace a known process results in a fluid layer of a sludge blanketwherein the suspension from the streaming liquid gets caught. Thefluidized layer of the sludge blanket in the separation space createsthe surface 14 of the sludge blanket above the level of the lowercollecting tube 3 for withdrawing the thickened suspension and under thelevel of the upper collecting tube 4 for withdrawing liquid withoutsuspension, while above the sludge blanket surface 14 a layer of liquidwithout suspension is located (FIGS. 1, 2).

It can be summarised that the flocculating suspension gets separatedfrom liquid by filtration in the fluidized layer of the sludge blanketwherein the flocks are created of the separated suspension and thefluidization is maintained by the upward flow of liquid. The liquid withsuspension enters the fluidized layer from the bottom and the liquidfreed from suspension is withdrawn above the surface 14 of the sludgeblanket represented by an interface between the fluidized layer and theliquid without suspension. The separated thickened suspension in form offlocks from the sludge blanket is withdrawn from the zone of thefluidized layer, while the velocity of upward flow in the fluidizedlayer essentially decreases in the upward direction.

The layer of sludge blanket above the level of withdrawing the thickenedsuspension operates as a partially fluidized sludge blanket wherein thethickened suspension further densifies, namely agglomerates of thickenedsuspension are formed and then withdrawn. The layer of sludge blanketunder the withdrawal level of thickened suspension operates as a fullyfluidized sludge blanket wherein the liquid flow is uniformlydistributed into the partially fluidized sludge blanket. Suchdistribution is due to the fact that the fluidized layer functions asporous environment the resistance of which distributes the flow,especially the upward flow, to the whole through-flow profile.Consequently, in the bottom fluidized layer of the fully fluidizedsludge blanket the stream of suspension gets distributed into the wholeprofile of the separation space, thus entering uniformly the fluidizedlayer of the partially fluidized sludge blanket. In analogy, close tosurface 14 of the sludge blanket the flow is uniformly distributed inthe whole area.

Separator 1 being connected by inlet 5 with the oxic space 16 which isconnected via connection 18 with the anoxic space 17, the overflow 9maintains the constant surface 10 of water in the whole tank 15.Accordingly, exactly the same volume of liquid that has entered tank 15through inlet 26 of waste water (FIG. 3) will flow out of tank 15through the upper collecting tube 4 and holes 6 in the same and furthervia discharge 8 over overflow 9. If the volume of water withoutsuspension having flown through discharge 8 from the separation space isQ_(o), and the volume of thickened suspension withdrawn byre-circulation pump 12 from the separation space is Q_(s), then thevolume of water with suspension that comes through inlet 5 into theseparation space equals Q_(o)+Q_(s). If the concentration of suspensionin the water flowing into the separation space through the inlet 5 is C,whereas the concentration of thickened suspension that is beingwithdrawn is C_(s), then the volume of suspension having come into theseparation space is C(Q_(o)+Q_(s)), whereas the volume of suspensionthat is withdrawn from the separation space is C_(s)Q_(s). In a steadycondition both volumes shall be equal and, accordingly, it holds for theconcentration of withdrawn thickened suspension in steady state:C_(ss)=(Q_(o)+Q_(s))/Q_(s). If the concentration of withdrawn thickenedsuspension is less than C_(ss), the volume of suspension in the sludgeblanket grows and due to that the surface 10 of sludge blanket rises, ifthe concentration of withdrawn thickened suspension is more than C_(ss),the volume of suspension in the sludge blanket drops and the surface 10of sludge blanket sinks. All amounts Q are specified in volume units perunit of time, such as cubic meters per hour, whereas the concentrationsare specified, e.g., as kg per cubic meter. Accordingly, the height ofsurface 14 of the sludge blanket varies and depends upon mass balance,in the same way as in the partially fluidized sludge blanket. In acertain range of parameters a sludge blanket has auto-regulatingproperties: the concentration of withdrawn thickened suspension C_(s)grows along with rising height of surface 14 of the sludge blanket, anddue to that, for a certain adjusted value of Q_(s) and the given valueQ_(o) the surface 14 of the sludge blanket will automatically stabiliseat a level allowing to fulfil the condition C_(s)=C_(ss). The appliedsymbols should be understood as follows:

-   C concentration of suspension in the activation mixture flowing into    the separation space-   Q_(o) volume amount of water without suspension flowing out of the    separation space-   Q_(s) volume amount of thickened suspension withdrawn from the    separation space-   C_(s) concentration of withdrawn thickened suspension-   C_(ss) concentration of withdrawn thickened suspension in steady    state.

Density streams with thickened suspension that flow under surface 14 ofthe sludge blanket along the inner side of the inclined outer wall 2 ofseparator 1 downwards, get down to the collecting tube 3 for thewithdrawal of thickened suspension, wherefrom they are sucked away bythe operation of the re-circulation pump 12. Since the holes 7 in thecollecting pipe serving for the withdrawal of thickened suspension arelocated at the upper side, the density streams above the collecting tube3 are subject to withdrawal. Such arrangement reduces the dilution ofwithdrawn thickened suspension.

A theoretically feasible limit for maximum flow velocity at the heightof surface 14 of sludge blanket corresponds with a velocity of about2–2.2 mph, during which the fully fluidized sludge blanket starts beingconverted to a partially fluidized sludge blanket, i.e. 50 percent ofthe currently achieved velocities 4–4.5 meters per hour in a fullyfluidized sludge blanket.

Experiments with the described apparatus wherein the throughflow area ofseparation space closely under the level of withdrawing the thickenedsuspension through the collecting tube 3 amounted to 25 percent of thearea of the separation space at the withdrawal level of liquid withoutsuspension through collecting tube 4 showed the maximum flow velocity atthe surface 14 of the sludge blanket in this apparatus to be within therange of 1.6–1.9 mph. In case of exceeding this value the sludge blanketwould already flow over into the withdrawal means of purified liquid.The consequence is an approximately doubled performance as compared withhitherto known equipment with partially fluidized sludge blanket. Theexperiments show to be preferable if the volume amount of thickenedsuspension removed by re-circulation pump 12 equals approximately doublethe volume amount of water without suspension that has flown awaythrough discharge 8, i.e. Q_(s)=approx. 2 Q_(o).

Since excess thickened suspension is removed from the sludge blanket inthe zone of its outer circumference in the described apparatus, withoutfalling out through inlet 5, the throughflow area of inlet 5 can besmaller than in the known equipments with partially fluidized sludgeblanket and, accordingly, the sludge blanket under the level ofwithdrawing the thickened suspension through collecting tube 3 canfunction as a fully fluidized one. This allows to inhibit the effect offalling out of the sludge blanket during lower onflow of suspension,which currently limits the scope of application of a partially fluidizedsludge blanket. In order to allow the sludge blanket under thewithdrawal level of thickened suspension to function as a fullyfluidized one, the flow velocity of water at the entrance into thesludge blanket shall comply with values for a fully fluidized sludgeblanket, i.e. it shall be within the range of 2 to 6 centimetres persecond. Considering the volume amount of re-circulated suspension andthe output of the apparatus, it is preferable to arrange the area ofinlet 5 so as to be larger than 3 percent and smaller than 6 percent ofthe area of the separation space at the level of withdrawing the liquidwithout suspension through way of collecting tube 4.

The volume amount of withdrawn thickened suspension is in the range of1.5 times to 3 times the volume amount of water without suspensionwithdrawn above the surface of the sludge blanket.

In the oxic space 16 and the anoxic space 17 of the reactor forbiological activation treatment of waste water, under the presence ofactivated sludge returned by re-circulation pump 12, the knownactivation treatment of waste water that is brought to the reactor bythe inlet 26 of waste water is performed, the purified water flowingaway by discharge 8 over the overflow 9. If the waste water containscompounds of nitrogen, such as sewage, the anoxic space 17 functions asa front-end de-nitrification space wherein the nitrates are reduced togaseous nitrogen. The mentioned nitrates formed by oxidation of nitrogencompounds in the oxic space 16 are returned into the anoxic space 17 inthe water that flows back from the oxic space 16 over separator 1together with the returned activated sludge through outlet 20 ofre-circulation pump 12. The above described arrangement of inlet 26 ofwaste water and the outlet 20 of re-circulation pump 12, together withthe flow induced by agitator 27 and channelled by deflecting walls 28lead, in a part of the anoxic space 17, to the creation of anaerobicconditions supporting the biological removal of phosphorus, while thedescribed location of connection 18 ensures that the brought waste watershall pass through the whole anoxic space 17 prior to flowing over intothe oxic space 16.

If the operation of the apparatus is interrupted, such as due to adropout of power or during an outage, the fluidization of the sludgeblanket is interrupted, the sludge blanket sediments and the settledactivated sludge accumulates in the zone of inlet 5 to separator 1. Ifthe interruption takes a longer time, the settled activated sludgeassumes a gel structure, which can result in a plug in the zone of inlet5 preventing to resume the function of the apparatus when the operationis restarted. That is why pressure water and pressure air are introducedinto counter-cone 22 upon restarting the operation. Both media areinjected through openings 23 in the upper part of counter-cone 22,bringing about intensive turbulence that breaks the layers of settledsludge and cleans the zone of inlet 5 into separator 1. In addition tothis function the counter-cone 22 has yet another purpose residing indirecting the flow under the inlet 5 into separator 1 for preventing thesedimentation of suspension on the bottom of tank 15 under the centre ofinlet 5.

EXAMPLE 2

The second example of embodiment of the apparatus according to theinvention is illustrated in FIGS. 4 and 5. Separator 1 is, in analogywith example 1, essentially limited by the upward widening conical wall2. The bottom part of separator 1 accommodates a conical inner wall 29that is attached to the bottom edge of outer wall 2 with its bottom edge(FIG. 4). The inner wall 29 limits also the space that is broadening inthe upward direction and reaches to the level of one third to one halfof the height of separation space. The separation space, accordingly, islimited by inner wall 29 in the bottom part of separator 1 and by outerwall 2 in the upper part of the separation space. Thus the separationspace is a part of the inner space of separator 1, which can be alsoexpressed by saying that the inner space of separator 1 contains aseparation space. The outer wall 2 above the upper edge 30 of the innerwall 29 has conical shape, whereas under the level of the upper edge 30it has the form of an elliptic canopy and its inclination in this partdecreases from 52°–60° down to 30°–40°.

The zone between the outer wall 2 and the inner wall 29 creates athickening space 31 of the suspension provided, in its bottom part, witha withdrawal of thickened suspension in form of collecting tube 32 woundto form a circle. This collecting tube 32 has preferably circularsection and forms also a supporting structure bearing at its outside thebottom edge of outer wall 2 and at the inside the bottom edge of innerwall 29. The bottom edge of inner wall 29 creates an entrancerepresenting inlet 5 into the separation space of separator 1. The notillustrated openings in the collecting tube 32 for withdrawing thethickened suspension are performed at the bottom edge of outer wall 2.The collecting tube 32 is connected via tube 11 to the re-circulationpump 12 similarly as in example 1.

It can be summarised that the bottom part of the separation space islimited by at least one at least partially inclined inner wall 29, thespace between the bottom part of outer wall 2 and inner wall 29 creatingthe thickening space 31. The gap, or possibly the area of the gapbetween the upper edge of this inner wall 29 and the outer wall 2 havingthe form of annular ring in this example, represents the removal spot ofthickened suspension where the thickened suspension is withdrawn fromthe separation space. This gap forms also the entry to the thickeningspace 31 the bottom part of which is provided with means for withdrawingthe thickened suspension.

The upper part of outer wall 2, in analogy with example 1, accommodatesmeans for withdrawing liquid without suspension in form of an insertedcircularly wound collecting tube 4 of triangular section with openings 6in the inclined inner side for withdrawing liquid without suspension.The collecting tube 4 mouths into discharge 8 wherein the overflow 9 isinstalled for maintaining constant surface 10 of water in separator 1.

The reactor for biological activation treatment of waste wateraccommodating the described apparatus according to example 2 is the sameas in example 1. The apparatus according to example 2 works in the sameway as the apparatus according to example 1, with the only differencethat the density streams with thickened suspension that flow undersurface 14 of the sludge blanket along the inner side of the inclinedouter wall 2 downwards, flow at the level of the upper edge 30 of theinner wall 29 through the annular ring between this upper edge 30 andthe outer wall 2 into the thickening space 31. Here a further thickeningof the suspension takes place prior to its being sucked away byre-circulating pump 12 through the holes in the collecting tube 32. Thisthickening takes place due to the fact that the diluting effect of thecounter-flow of liquid entering the separation space is inhibited in thethickening space 31 and, accordingly, during the flow of density streamsalong the inner side of outer wall 2 downwards the densifying effectprevails. The liquid or, possibly, the diluted suspension that has beenpushed out of the density stream during the thickening process, flowsaway along the outer side of the inclined inner wall 29 upwards, thusreturning into the sludge blanket. This is supported by the flow ofliquid with suspension in the separation space that joins, above theupper edge 30 of inclined inner wall 29, with the flow of liquid thathas been pushed out. Due to higher density of suspension removed byre-circulation pump 12 and, accordingly, also higher concentration C_(s)of thickened suspension, under the same values of Q_(o) and Q_(s), theconcentration C of suspension in the water flowing into the separationspace through the inlet 5 is higher than in example 1. Since, due to thethickened suspension being sucked away by collecting tube 32 at thebottom of thickening space 31, the overall flow in the thickening space31 is falling, thus supporting the downward movement of suspension, theinclination of outer wall 2 in this region can be smaller than theinclination in the upper part of separator 1. Experimental experiencerelating to sliding of flocculating suspension along the inclined wallsin the presence of downward flow has shown that in case of 30° to 40°inclination of the walls no sediments of suspension flocks are seen onthese walls and, consequently, this inclination has been applied for thebottom part of outer wall 2 in the bottom part of thickening space 31.

EXAMPLE 3

The third example of apparatus according to the invention is illustratedin FIGS. 6 and 7.

This embodiment has a longitudinal separator 1 in form of an upwardwidening prism created by inclined outer walls 33 and 34 of which eachaccommodates at middle height, similarly as in example 1, collectingtubes 35 and 36 for withdrawal of thickened suspension that areconnected with the re-circulation pump 12. The inner space of separator1 represents the separation space. The collecting tubes 35 and 36 arepart of the inclined outer walls 33 and 34 whose parts are attached tothese tubes. In the place of collecting tubes 35 and 36 the upper partsof outer walls 33 and 34 are shifted against the bottom parts so thatseparator 1 and, consequently, also the separation space, get broadenedby a jump in this place. The collecting tubes 35 and 36 for thewithdrawal of thickened suspension are provided with holes 37 that areprovided in the sides of tubes 35 and 36 that are turned to the upperpart of the shifted inclined outer walls 33 and 34.

The bottom edges of inclined outer walls 33 and 34 create the inlet 38into separator 1 in form of an oblong rectangular gap. At the level ofinlet 38 the inclined outer walls 33 and 34 are provided with rinsingpipes 39 and 40 having holes 41 for the inlet of water and air at leastin two rows.

The upper part of separator 1 accommodates collecting tubes 42 and 43for withdrawing liquid without suspension having overflows 9 in analogywith the preceding embodiment. All overflows 9 are adjusted to the samelevel in order to ensure uniform outflow of liquid. The collecting tubes42 and 43 are provided with holes 48 at their tops for the inlet ofpurified water (FIG. 7). The upper edge of inclined outer walls 33 and34 carry inlet pipes 44 and 45 serving for the inlet of pressure air.

At least some functional tubes or, possibly, all functional tubes in theouter walls 33 and 34, i.e. the collecting tubes 35 and 36 serving forthe withdrawal of thickened suspension, the collecting tubes 42 and 43for withdrawing liquid without suspension, inlet pipes 44 and 45 servingfor the inlet of pressure air, and the rinsing tubes 39 and 40, arecomponent parts of the supporting structure of the inclined outer walls33 and 34. To this supporting structure the wall elements are attachedthat create the surface of inclined outer walls 33 and 34. The describedexample of apparatus for the separation of flocculating suspension is apart of the reactor for biological activation treatment of waste water,that consists, in this embodiment, of tank 15 divided to an oxic space16 and an anoxic space 17 that communicate through connection 18. Theoxic space 16 accommodates the described separator 1 whose inlet 38 thuscommunicates with the oxic space 16, whereas the outlet 20 ofre-circulation pump 12 mouths in the anoxic space 17.

Separator 1 is closed by vertical fronts that are created by parts ofthe partition wall 19 dividing the tank 15 to an oxic space 16 and ananoxic space 17, and a part of the front wall of tank 15 that is notvisible in FIGS. 6 and 7.

Adjacent to the bottom edge of one inclined outer wall 34 a closing wall46 is arranged that reaches down to the bottom of tank 15, to thepartition wall 19 and to the front wall of tank 15. In this way the partof the oxic space 16 between the right inclined outer wall 34 and thewalls of tank 15 is closed, while communicating with other spaces onlythrough the connection 18 in partition wall 19 and the passages 47 (FIG.7) that are arranged essentially at the bottom of tank 15 in the closingwall 46 in its part that is most distant from the anoxic space 17. It isalso worth mentioning that partition wall 19 together with the rightinclined outer wall 34 divide the oxic space 16 in two parts that areinterconnected with passages 47. The first part of the oxic space 16communicates through connection 18 with the anoxic space 17 and theother part of the oxic space 16 communicates with separator 1 throughthe inlet 38. The closing wall 46 can be also attached to the leftinclined outer wall 33, yet in such case the connection 18 should beperformed at the left hand side, since both these elements should belocated in the same part of the oxic space 16.

The oxic space 16 is further provided with aeration elements 24connected to the inlet pipe 25 of pressure air. The arrangement andequipment of the anoxic space 17 is the same as in the precedingexamples.

The described third exemplifying apparatus works similarly as the abovedescribed first exemplifying apparatus with the difference that theclosing wall 46 eliminates shortcuts of flow in the oxic space 16 and,accordingly, the activation mixture after having come through connection18 must flow through the first part of oxic space 16 first, and onlyafter having flown through passages 47 it can proceed from the secondpart of oxic space 16 through the inlet 38 into the separation space.Another difference is based upon the fact that cleaning of the zone ofinlet 38 into the separator 1 after an interruption of operation isperformed by introducing pressure air and pressure water into therinsing pipes 39 and 40 where, under simultaneous introduction of bothmedia, the air streams through holes 41 in the upper part of rinsingpipes 39 and 40, whereas water is ejected through holes 41 that areperformed in the bottom part of rinsing pipes 39 and 40.

EXAMPLE 4

The fourth exemplifying embodiment of the apparatus is illustrated inFIGS. 8 and 9.

Separator 1 according to this example is substantially limited by upwardwidening inclined outer walls 50 and 51. The bottom part of separator 1accommodates inclined inner walls 52 and 53 whose bottom edges areattached to the bottom edges of outer walls 50 and 51 (FIG. 8), which isan analogy to the embodiment according to example 2. The inner walls 52and 53 enclose also the space that widens upwards and reaches to thelevel of one third to one half of the height of separator 1. Theseparation space wherein the actual separation takes place, accordingly,is limited by inner walls 52 and 53 in the bottom part of separator 1,and by outer walls 50 and 51 in the upper part of separator 1. The outerwalls 50 and 51 are inclined within the range of 52° to 60° above thelevel of the upper edges 54 and 55 of the inner walls 52 and 53. Underthe level of the upper edges 54 and 55 of the inner walls 52 and 53, andapproximately at the level of withdrawing thickened suspension, theouter walls 50 and 51 are provided with inclinations within the range of30° to 40°.

The zone between the outer wall 50 or 51 and the inner wall 52 or 53creates the thickening space 56 of suspension, while the bottom part ofthis space is provided with withdrawal of thickened suspension in formof collecting tubes 57 and 58. The entry to the thickening space 56 atthe level of the upper edges 54 and 55 of the inner walls 52 and 53 hasthe form of two rectangles and represents the withdrawal spot ofthickened suspension from the separation space.

The collecting tubes 57 and 58 serve also as a supporting structures forthe outside to which the bottom edges of walls 50 and 51 are attachedand for the inside carrying the bottom edge of inner walls 52 and 53.The bottom edge of inner walls 52 and 53 together with partition wall 19and the front wall of tank 15 create a rectangular inlet openingrepresenting the inlet 59 into separator 1, and thus into the separationspace. The openings 60 in the collecting tubes 57 and 58 for withdrawingthe thickened suspension are performed close to the bottom edge of outerwalls 50 and 51. The collecting tubes 57 and 58 communicate via tube 11with the re-circulation pump 12 in analogy to example 2.

Similarly as in example 3 adjacent to the bottom edge of one inclinedouter wall 51 the closing wall 46 is arranged that reaches down to thebottom of tank 15, to the partition wall 19 and to the front wall oftank 15 and has the same purpose as in example 3. Also the embodiment ofpassages 47 is the same. For better orientation in the picture thepassages 47 and the closing wall 46 are illustrated only in FIG. 9, notin FIG. 8.

The upper part of the separation space houses the collecting tubes 61and 62 for the withdrawal of liquid without suspension. They areprovided with holes 48 for the inlet of purified liquid at their tops.The vertical parts (FIG. 9) of the collecting tubes 61 and 62 areconnected with the discharge tube 67 (FIGS. 8 and 9) of purified liquid,and namely at the spot where the inclined outer walls 50 and 51 arekinked (include an angle), and it also creates a part of the supportingstructure of the outer walls 50 and 51. The discharge tube 67 ofpurified liquid is arranged at the level of removal of thickenedsuspension from the separation space, which substantially correspondswith the level of the upper edges 54 and 55 of the inner walls 52 and53.

The collecting tubes 61 and 62 are provided with overflows 63. Alloverflows 63 are adjusted to the same level in order to ensure regularoutflow of liquid. The upper edges of the inclined outer walls 50 and 51accommodate the inlet pipes 64 and 65 for the inlet of pressure air thatare also part of the supporting structure of the outer walls 50 and 51.Close to bottom 21 of tank 15 the cleaning pipe 66 (FIG. 8) is arrangedthat is not illustrated in FIG. 9 in order to maintain goodunderstandability of the picture.

An exemplifying reactor for the biological activation treatment of wastewater accommodating the described exemplifying embodiment of anapparatus for the separation of flocculating suspension is basically thesame as according to example 3.

An embodiment according to example 4 works in analogy with the abovedescribed embodiment according to example 2, with the difference thatinstead of counter-cone 22 a cleaning pipe 66 that can function as arinsing pipe after having been connected with water and air supply, isused for cleaning the zone of inlet 59 into separator 1. Anotherdifference ensues from the fact that the closing wall 46 with passages47 directs the flow in the oxic space 16 in analogy with the precedingreactor according to example 3.

In addition to the described functional parts all exemplifyingembodiments use various, mostly not illustrated, supporting columns,supporting elements, and possibly further current design elements. Inall embodiments it holds that the separation space in separator 1essentially widens in the upward direction, and namely both above thelevel of withdrawal of thickened suspension, and underneath.

The method and apparatus for performing the method according to theinvention are not limited to the described examples only, but comprisealso all modifications that are obvious for those skilled in the artupon the basis of the described basic embodiments of the invention. Theupward widening separator 1 can contain, e.g., also a cylindrical orsimilar part, i.e. it need not widen continuously. Also the inner walls29, 52, 53 can be performed in a similar way. Only the prevailing partsof the functional tubes, especially the collecting tubes 3, 4, 32, 35,36, 57, 58, can be arranged at the walls of separator 1, whereas theremaining parts can be arranged inside or outside separator 1. However,it is important that at least the predominant part of collecting tubes3, 35, 36 for the thickened suspension should be arranged at the outerwall or outer walls of the separation space or, possibly, in its outerboundary zones.

In addition to that the collecting tubes 3, 35, 36 for the thickenedsuspension are arranged with their functional parts at ¼ to ¾ of theheight between the inlet 5, 38, 59 into the separation space and thelevel of withdrawal of purified liquid. Functional parts are understoodto be the parts of collecting tubes 3, 35, 36 in whose holes 7, 37 thethickened suspension enters directly.

The collecting tubes 32, 57, 58 in the thickening space 31, 56 serve forwithdrawal of the thickened suspension. They are preferably arrangedroughly at the level of inlet 5, 38, 59 into the separation space,however, they can be also accommodated slightly above or under the same.

INDUSTRIAL APPLICABILITY

The method and the apparatus according to the present invention areintended in particular for the separation of flocculating suspension inthe process of waste water treatment, and namely both for municipal orconurbation sewage and for smaller units, such as hotels or singlehouses. They are also suitable for treatment of waste water fromindustrial plants and mines, or from agricultural enterprises, such asliquid manure of farm animals.

LIST OF PARTS

-   1 separator-   2 outer wall of separation space-   3 collecting tube of angular section for withdrawing the thickened    suspension-   4 collecting tube of triangular section for withdrawing liquid    without suspension-   5 inlet created by entrance to the separation space-   6 holes in tube 4-   7 holes in tube 3-   8 discharge-   9 overflow-   10 water surface-   11 pipe-   12 re-circulation pump-   13 cylindrical end piece-   14 surface of sludge blanket-   15 tank-   16 oxic space-   17 anoxic space-   18 connection-   19 partition wall separating the oxic space from the anoxic space-   20 outlet of the re-circulation pump-   21 bottom of tank-   22 counter-cone-   23 holes in the counter-cone-   24 aeration element-   25 inlet pipe of air-   26 inlet of waste water-   27 agitator-   28 deflecting wall-   C concentration of suspension at the inlet of separation space-   Q_(o) volume amount of water without suspension flowing out from the    separation space-   Q_(s) volume amount of thickened suspension withdrawn from the    separation space-   C_(s) concentration of withdrawn thickened suspension-   C_(ss) concentration of withdrawn thickened suspension in steady    state

Example 2

-   29 inner wall-   30 upper edge of the inner wall-   31 thickening space-   32 collecting tube

Example 3

-   33 inclined outer wall-   34 inclined outer wall-   35 collecting tube-   36 collecting tube-   37 aperture-   38 inlet into separation space-   39 rinsing pipes-   40 rinsing pipes-   41 holes in the rinsing pipe-   42 collecting tubes for withdrawing liquid without suspension-   43 collecting tubes for withdrawing liquid without suspension-   44 inlet pipe for the inlet of pressure air-   45 inlet pipe for the inlet of pressure air-   46 closing wall-   47 passages in the closing wall-   48 holes in the collecting tube for withdrawal of liquid without    suspension

Example 4

-   50 outer wall-   51 outer wall-   52 inner wall-   53 inner wall-   54 upper edge of inner wall 52-   55 upper edge of inner wall 53-   56 thickening space-   57 collecting tube of suspension-   58 collecting tube of suspension-   59 inlet into separator-   60 openings in the collecting tubes 57 and 58-   61 collecting tubes of water without suspension-   62 collecting tubes of water without suspension-   63 overflow-   64 inlet pipe of pressure air-   65 inlet pipe of pressure air-   66 cleaning pipe-   67 discharge tube of purified water (FIG. 8)

1. Method of separating suspension for treatment of waste water,comprising introducing the suspension including wastewater into aseparator containing a fluidized sludge blanket wherein a flocculatingsuspension is separated from a liquid including said wastewater byfiltration in a fluidized layer of a sludge blanket wherein flocks arecreated from separated suspension and fluidization is maintained by arising stream of liquid, while liquid with suspension enters thefluidized layer from the bottom and the liquid freed from suspension isdischarged above the surface of the sludge blanket represented by aninterface between the fluidized layer and the liquid without suspension,and velocity of upward flow in the fluidized layer decreases essentiallyin the upward direction, wherein there is formed an upper partiallyfluidized sludge blanket and bottom fully fluidized sludge blanket,wherein the partially fluidized sludge blanket agglomerates of thickenedsuspension are established which move downward along an inclinedboundary resulting in a concentration of the thickened suspension intodensity streams which are withdrawn, and in the fully fluidized sludgeblanket liquid flow is distributed into the partially fluidized sludgeblanket, excess thickened suspension being withdrawn along an inclinedside boundary of the fully fluidized sludge blanket.
 2. Method accordingto claim 1, characterised in that the separated thickened suspensionremoved from the partially fluidized sludge blanket layer is forciblymoved downward while getting further thickened.
 3. Method according toclaim 1, wherein if a concentration of inflowing suspension exceeds 1 kgof dry matter per cubic meter, the velocity of upward water flowimmediately above the surface of sludge blanket is in the range of 1.6to 2.2 meters per hour.
 4. Method according to claim 1, characterised inthat a water flow velocity at the entrance to the sludge blanket iswithin the range of 2 to 6 cm per second.
 5. Method according to any oneof claims 1, 2, 3 and 4, characterised in that the volume of withdrawnthickened suspension makes 1.5 multiple to 3 multiple of the volume ofwater without suspension withdrawn above the surface of sludge blanket.